1. Field of the Invention
The present invention relates to fluid filtration assemblies which use filter leafs. More particularly, the present invention relates to a closed loop, crossflow fluid filter assembly having a pressurized input to create a turbulent crossflow of fluid over the filter media faces of the filter leafs which are mounted to an outtake, or filtrate, manifold which is, in turn, connected to a vacuum source. The present invention further relates to mounted grids having a fluid path therethrough to create turbulence and to maintain a proper spatial relation among the tank and filter media during backwash filter cleaning operations.
2. Description of the Relevant Art
Heretofore there have been provided fluid filtration assemblies using filter leafs carrying filter membranes or other filtering media of known porosity. These devices generally comprise:
a tank for receiving contaminated fluids,
filter leafs, which carry the filtering media, having an inside core for receiving and collecting filtered fluid, and connected to a clean fluid outlet external to the tank, and,
a sedimentation collecting portion of the tank with a sediment outlet.
Efficiency of filtration in these systems is directly proportional to the fluid volume opposing the filter membrane surface area. Factors impinging on this efficiency include: pressure differential between the inside and outside of the filter leaf, the vector of fluid flow over the membrane, the surface area of the filter media, and the porosity of the membrane. It is evident that a fluid vector directly opposing the surface of the membrane is most desired to provide maximum fluid pressure in the desired filtration path, i.e., perpendicular to the plane surface of the media. Also, the less porous the filter media, the more need for fluid pressure to help speed the process of passing the desired fluid through the filter media which presents a barrier to particles beyond the pore size of the media.
However, as particles are barred passage through the media they will accumulate thereon, clogging the pores and decreasing the usable surface area of the media. With a perpendicular flow, the fluid pressure will act to trap these particles on the media surface, soon resulting in decreased efficiency of filtration.
Heretofore, the filtration devices provided have sought to solve this problem by utilizing a lateral flow over the media face or utilizing a slow fluid flow rate through the tank and encouraging a perpendicular flow vector to the filter media by providing suction on the interior of the filter leaf core to create the proper pressure differential across the media face. Further, regular backwashing of the filter leafs is often utilized.
The known devices thus sacrifice efficiency through buildup of particulates on the media face or by not providing a maximum pressure differential across the media face.
Further, the known devices heretofore have been unnecessarily complicated in material and design through the addition of extra support fittings needed to maintain proper spatial relation between closely spaced filter leafs. The prior devices require strong mechanical attachment means on the leaf core to filtered fluid drain junction and/or additional support frames over the top of the leafs which also decreases fluid flow over the membrane surfaces.
Finally, when utilizing closely spaced filter leafs, scant attention has been paid to providing proper flow-through spacing means to prevent filter media from touching one another or the tank walls when the media bulge outward under the pressure of the backwash cleaning process, thereby resulting in trapped particles on the media face.
The present invention gains increased efficiency of filtration by providing a high velocity turbulent flow of fluid having vectors parallel, lateral, perpendicular, and oblique to the media faces. The flow established thereby acts to shear particulate buildup from the media face while maintaining a fluid cross flow in the desired path through the media. The desired fluid flow path is further encouraged in the present invention by providing a vacuum source to the core of the filter leaf, thereby increasing the pressure differential across the media face.
Flow-through grids are affixed throughout the tank to provide positional stability for the leaf filter media during backwashing processes and to enhance turbulent fluid flow during filtration.
U.S. Pat. No. 3,559,809 describes a non-pressurized input filter system having individual filter membrane units. It is primarily directed to a backwash flow system utilizing a tank for dirty fluid and a separate tank for clean fluid. The clean fluid flow lines utilize an in-line eductor to create suction for the filter membranes.
U.S. Pat. No. 2,013,776 describes a closed tank filter system for drycleaning systems utilizing individual filter units separated by wire rack devices. The flow may be input alternately from the top or bottom of the tank. No suction is applied to the filter units' central manifold, nor is provision made for directing pressurized flow between the filter membranes. A sediment trap is located in the bottom of the tank.
U.S. Pat. No. 4,519,903 discloses an open tank parallel filter leaf apparatus utilizing bilateral manifolds whose connective conduit is attached to a suction pump. The polluted fluid is input to a holding trough from whence it spills into the open tank. Beneath the filter leafs is a sedimentation tank portion. The filter units are comprised of opposing grids, with holes defining channels through each section, attached to a lateral collection pipe. The grid and pipe assembly is then completely covered with a filter bag.
A filter system similar to U.S. Pat. No. 4,519,903, but having a series of pressurized input fluid conduits disposed above the parallel spaced filter leaves is also known to applicants.
U.S. Pat. No. 3,623,614 discloses a filter leaf core having a pair of studded outer sheets bonded to a resilient core. The outer sheets are overlayed by filter screens. Screens and core are encased in a fluid conductive frame which empties into a collection pipe on the frame bottom.
While it is evident from the foregoing that there are known many arrangements of filter leaf filtration devices, all of the known references present elaborate structural requirements resulting in filter systems that are harder to build, harder to clean, result in larger amounts of particulate buildup on the membrane faces and thus are prone to more frequent maintenance than the current invention.
It is believed by applicants that no existing system of filter leaf filtration offers the combined advantages of modularity, versatility, ease of manufacture, high filtering rate, low filter media clogging, and efficiency of back wash mechanisms and ease of cleaning the structure, presented in the invention described herein.